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View Full Version : Elevator Trim: Realistic Modelling?



Flightvector
07-21-2005, 11:59 PM
I have read many requests on the removal of the elevator trim cheat, but no recommendations or clear insight on its modelling. I would like to provide some input to agree that it has not been modelled realistically, hence these issues.

Firstly, I haven't had the time to fly PF for a while, so if this was modified extensively in 4.01, forget all of this.

Elevator trim is almost always an aerodynamic control mounted on the elevator itself. The tab's motion forces the elevator to deflect. The trim tab deflects downwards to move the whole elevator up and vice versa (Think of trim as the elevator's elevator).

In all cases where the trim tab is on the elevator, it NEVER changes the elevator's physical range of motion. Also, trim does not enhance maximum full detente elevator lift moment force at all, but rather, diminishes it, if ever so slightly.

The reason for this diminishing effect is clear: For full nose up trim, the tab is deflected downwards full stop, and the moment generated from this pushes the elevator upwards. Granted, it will be a lot easier to pull backwards on the stick. But notice the trim tab represents 10% or so of the elevator surface that is pointing in the opposite direction; it actually increases the positive lift of the horizontal stabilizer (we want negative lift for nose up pitch). In fact, I believe it is as bad as or worse than having 10% of your elevator cut off.

So, the trim should be modelled as so:
Even at full nose down trim, you should still be able to achieve maximum combat turn rate if not even slightly more than when at full nose up trim.

Trim should act like a constant offset joystick input without affecting maximum nose up or nose down pitch moment.


Keep in mind that for airplanes where trim adjusts the angle of the entire horizontal stabilizer, called stabilator trim (Me-109), trim can be used to cheat, per se, since it does increase elevator authority, acting on superposition. For such planes, such an exploit may have been possible given a fast enough trim crank.

There is also one limitation to my proposal; at 300 knots, it may be physically too difficult to pull on the stick without trim, and this might also make this trim exploit possible. But since corner speed is the most controversial area, trim might not be necessary to achieve full deflection at these speeds. BUT, physical ability and strength have never been modelled in IL2 or PF, so this would be a nonissue in that case.

Please don't think I am talking down to anyone, if my statements seem overly strong, I am only trying to make sure I am heard. But I do have an aerodynamic basis for my conclusions if anyone must hear it.

NonWonderDog
07-22-2005, 04:15 AM
Originally posted by Flightvector:
Firstly, I haven't had the time to fly PF for a while, so if this was modified extensively in 4.01, forget all of this.

Yep.

Next. http://forums.ubi.com/groupee_common/emoticons/icon_wink.gif


Honestly, though, the trim seems a lot better now. Try it, you'll like it. Move the elevator back and forth on the ground to see exactly how it reacts. It doesn't really behave how it should on the ground, but just pretend you have a strong headwind. http://forums.ubi.com/groupee_common/emoticons/icon_razz.gif

The German planes that should have a trimmable stabilizer don't appear to have one (or the effects of one), but that's probably a pre-emptive strike against the whining more than anything. I would like to see this modelled, though.

F19_Ob
07-22-2005, 05:34 AM
Originally posted by NonWonderDog:

The German planes that should have a trimmable stabilizer don't appear to have one (or the effects of one), .

wich ones?

109's only have elevator trim for the pilot to adjust and have fixed trimtabs for the other surfaces wich are set by the groundcrew to levelflight at cruisingspeed.

Other than that the only concern I have is if trim can be used as a noticeable cheat online by enabling it to a slider and get better turning performance than was possible.
That was why it was given some delay in the 3.04 patch.

Some claim it's a cheating aid again but I can't verify or deny that because I haven't flown 4.01 online yet.

perhaps someone can shed some light on this?

Jetbuff
07-22-2005, 09:13 AM
Originally posted by Flightvector:
There is also one limitation to my proposal; at 300 knots, it may be physically too difficult to pull on the stick without trim, and this might also make this trim exploit possible. But since corner speed is the most controversial area, trim might not be necessary to achieve full deflection at these speeds. BUT, physical ability and strength have never been modelled in IL2 or PF, so this would be a nonissue in that case.
I'm sorry but you are mistaken. IL-2, from the beginning, has modelled pilot strength. Max deflection on the joystick = max effort rather than max deflection on the virtual-stick.

A.K.Davis
07-22-2005, 09:29 AM
Originally posted by F19_Ob:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by NonWonderDog:

The German planes that should have a trimmable stabilizer don't appear to have one (or the effects of one), .

wich ones?

109's only have elevator trim for the pilot to adjust and have fixed trimtabs for the other surfaces wich are set by the groundcrew to levelflight at cruisingspeed. </div></BLOCKQUOTE>

In Fw-190s, the angle of the horizontal stabilizers was adjusted, rather than the elevators. In-game, only the elevators move. I think this is what he was referring to.

AerialTarget
07-22-2005, 02:21 PM
Originally posted by Jetbuff:
I'm sorry but you are mistaken. IL-2, from the beginning, has modelled pilot strength. Max deflection on the joystick = max effort rather than max deflection on the virtual-stick.

Yes, but maximum pilot effort in the game is eighty pounds, which is absolutely ridiculous. Not only is that only one hand, but it's such a womanly figure for one hand! I can pull more than that, and I'm a hundred twenty five pound five foot tenner!

Rest assured that much, much better results at pulling up at high speeds are possible in real life. You can do it more than twice as good in real life, if you have at least as much strength as I have. So yes, he is correct - the trim system is very, very unrealistic.

NonWonderDog
07-22-2005, 10:47 PM
Sure it's only eighty pounds? I've never seen an official figure, only random guesses from players. These random guesses usually range between 50-150 pounds pull force.

Eighty pounds would be awfully stiff even for a recurve bow, though, and you can put a lot more force into a bow with one arm than you can into a control stick. It's not an unreasonable figure for one hand at all. With two hands you should be able to pull more... for a minute or two. Since the pilot never gets tired in the game, it really doesn't seem all that rediculous if it *is* in fact limited to eighty pounds. I don't really know how good or bad the cockpit ergonomics were, though; the closest I've ever been to sitting in a warbird cockpit was a 3/4 scale Mustang replica.

WWMaxGunz
07-23-2005, 12:35 AM
On the one hand I've always had to use two arms to pull a bow, it's easier when you pull
one against the other. On the other hand, it's not just about pulling weight but also
about holding it while moving it around under tight control while undergoing as many G's
as that pull is getting you which is the crux difference between lifting a weight and
working one in a hard moving environment.

ImpStarDuece
07-23-2005, 02:29 AM
Originally posted by AerialTarget:

Yes, but maximum pilot effort in the game is eighty pounds, which is absolutely ridiculous. Not only is that only one hand, but it's such a womanly figure for one hand! I can pull more than that, and I'm a hundred twenty five pound five foot tenner!

Rest assured that much, much better results at pulling up at high speeds are possible in real life. You can do it more than twice as good in real life, if you have at least as much strength as I have. So yes, he is correct - the trim system is very, very unrealistic.


You must have arms the size of the Govenor of Claifornia.

Seriously, I use a 70 pound, 70 centimetre draw recurve bow for archery and it takes a HEAP of effort to hold an arrow in place. After two sets of 30 arrows my I begin to get the trembles in my right arm. Two more sets and I'm usually done. I'm not small either; 190 cm, 85 kg (6'3", 190lbs) . And I have plenty of space to stretch out and move about in. The tight confines of a cockpit are not condusive to pushing/pulling very high amounts of force.

Add G forces to this as well. All of a sudden you arm weights 3,4,5 times what it did previously. Its not easy at all.

Skalgrim
07-24-2005, 05:00 AM
A wrong trimm 109 was almost not to recover by dive with 750km/h, but with the right trimm it was easy, it was so easy the pilots has fear to get blackout, but it was not need so many trimm like in game,

only 1-1,5 deg from german test


Originally posted by ImpStarDuece:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by AerialTarget:

Yes, but maximum pilot effort in the game is eighty pounds, which is absolutely ridiculous. Not only is that only one hand, but it's such a womanly figure for one hand! I can pull more than that, and I'm a hundred twenty five pound five foot tenner!

Rest assured that much, much better results at pulling up at high speeds are possible in real life. You can do it more than twice as good in real life, if you have at least as much strength as I have. So yes, he is correct - the trim system is very, very unrealistic.


You must have arms the size of the Govenor of Claifornia.

Seriously, I use a 70 pound, 70 centimetre draw recurve bow for archery and it takes a HEAP of effort to hold an arrow in place. After two sets of 30 arrows my I begin to get the trembles in my right arm. Two more sets and I'm usually done. I'm not small either; 190 cm, 85 kg (6'3", 190lbs) . And I have plenty of space to stretch out and move about in. The tight confines of a cockpit are not condusive to pushing/pulling very high amounts of force.

Add G forces to this as well. All of a sudden you arm weights 3,4,5 times what it did previously. Its not easy at all. </div></BLOCKQUOTE>